Process for separating sulphur dioxide from gaseous mixtures



Sept 4,1934. M. c. BoswELL- 1,972,074

PROCESS FOR SEPARATING SULPHUR DIOXIDE FROM GASEOUS MIXTURES Filed sept. 8, 1930 OMP/F5530@ jo nvenfor Patented Sept.` 4, 1934 PROCESS FOR SEPARATING s U L P HU a DioxmE FROM GAsEOUs Mix'rUnEs Maitland C. Boswell, Toronto, Ontario,

Canada.

Application september 8,1930, seria1No.4so,4so

1 claim. (ci. zs-rm)v This invention relates particularly to the sepaever, the possibility is not excluded of the formaration of sulphur dioxide from gaseous mixtures tion of some addition product of quinoline or in which it is present in relatively small proquinoline hydrate and sulphur dioxlde'or sulportions. phurous acid.

5 It has been proposed to separate the sulphur I have found that various mixtures of quino- 60 dioxide. by effecting its solution in water or some line and water and various concentrations of waother liquid or solution. The high vapor pressure ter vapor in the gas may be employed, a very conof sulphur dioxide and the slow rate at which venient and emcient ratio of quinoline to water it is absorbed by liquids, however, renders such being secured by agitating quinoline and water 1o processes troublesomein operation, as very large at ordinary atmospheric temperature and sep- 65 quantities ofliquid must therefore beused. arating mechanically the two layers of liquid My object, therefore, is to devise a method of formed on standing. Y separating the sulphur dioxide by means of which When the gaseous mixture containing sulphur the sulphur dioxide may be removed rapidly and dioxide is agitated with the quinoline and water,

substantially completely, even from very dilute the sulphur dioxide is taken up and the solution 70 mixtures and with the use of a comparatively becomes more or less viscous. small quantity of Vehicle. When water is used in the process I have found I attain my object by employing as the-vehicle that a solution or suspension of the quinoline for the removal of the sulphur dioxide a liquid and water in glycerol, petroleum or other solvent reagent, or solution of a solid reagent, with which or diluent medium of quinoline sulphite dimin- 75 Ithe sulphur dioxide actually combines but from ishes the viscosity ofthe reaction product with which it maybe afterwards readily dissociated by sulphur dioxide, and these diluting media may the action of heat. be used in the process. K

The reagents I employ are the'bases of the The quinoline-waterfsulphur dioxide reaction 25 pyridine, quinoline, isoquinoline and acridine product gives off practically no sulphur dioxide 80 series and also their hydrogenation products as below 70 C. and at atmospheric pressure. Above well as commercial bases containing them, such 70 C. the gases are given off more vand more as the higher boiling fractions of the bases of rapidly and at 100 to 110 C. the dissociation is coal tarv and of bone oil. Of the pure bases so rapid that about three quarters of the sulphur quinoline and hydrogenated quinoline are, on acdioxide absorbed may be recovered very quickly,l 85 count of their lower cost and high elciency, the the remainder being recoverable more slowly. best adapted at present for use in the process. The low vapor pressure of quinoline at the tem- I have found that dry quinoline will absorb peratureof absorption (about 30 C.) maintains considerable quantities of sulphur dioxide from a the amount of quinoline vapor in the exit gases gaseous mixture when the percentage of sulphur at -a very low value. This escaping quinoline is 90 dioxide is high but when the percentage is low recovered in a washer containing dilute acid the absorption is not sufliciently eiective to be `from which the quinoline can be recovered from commercially practicable. I have further found, time to time when sufllcient has accumulated. however, that quinoline containing water is ca- The process of this patent consists in passing 40 -pab1e, at ordinary atmospheric temperatures and the gas containing sulphur dioxide, preferably 95 pressures of very rapidly and completely removfreed from dust and sulphur trioxide and cooled ing sulphur dioxide from gaseous mixtures even to a temperature preferablyv below 30 C., al-

at very low concentrations of sulphur dioxidein though higher temperatures may be used, the gas. through towers or scrubbers Y containing, or

VThe amount of sulphur dioxide absorbed by a through which is passing, at a temperature pref- 100 given weight of quinoline does not depend on the erably below 30 C. (although temperatures conpartial pressure of the sulphur dioxide in the gas. siderably higher may be used), the prepared re- That is a chemical reaction occurs between the agent. The exit gases 'which contain a small quinoline-water complex and sulphur dioxide. amount 'of the vapor of the base used are passed 50 The ratio of quinoline to sulphur dioxide'in the through a tower or washer where the gas meets 105 compound formed as indicated by measurement dilute acid, such as dilute sulphuric acid, or hy-v is approximately two molecules of quinoline to drochloric acid in order to remove the base. At

one molecule of sulphur dioxide. This points to intervals this acid solution of base is treated with the formation of a normal sulphite of quinoline, lime or other inorganic base for the recovery-of the quinoline acting as a non-acid base. IHowthe organic base, or if sulphurous acid is. used 110 the organic base may be recovered by heating to expel the sulphur dioxide when thefree organic base separates. The liquid from the washing tower or scrubber and holding the'sulphurdioxide is run into a heatervwhere it is heated to a sufficient temperature to drive off the sul-l Aproduct'of the base and sulphur dioxide or of base, water and sulphur dioxide. This base may be recovered from time to time. The sulphur dioxide may next pass to a compressor for collection as compressed gas or liquid sulphur dioxide. The base or base-water mixture is nowmade to ow throughva cooler so as to lower its temperature to about 30 fC. and ispumped into washing towers or scrubbers for the removal of sulphur dioxide from more gas.

By using several washing towers or scrubbers thewaste gas containing sulphur dioxide can be run through one or more of these while the liquid saturated with sulphur dioxide is being run out of one or more other towers or scrubbers into the heater and while the sulphur dioxide is being recovered and the base or its solution is being cooled and made ready to be pumped back again into the towers or scrubbers. Or the process can be made continuous, cooled base being continuously pumped to the washing towers orscrubbers Leraars which gaseous mixture' containing sulphur dioxide is led to the absorber 2 containing the vehicle by which the sulphur dioxide is picked up. 3 is a pipe connecting the absorber 2 with a.

' washer 4 in which any of the reagent carried over is'recovered.v lBy means of the pipe 5 the liquid containing thesulphurdioxide is led to the heater 6. .From the heater 6 the gaseous sulphur dioxide is led, by means of the pipe 7, to the cooler 8, from which a pipe 9 leads to the compressorl. The liquid from which the sulphur dioxide has been expelled is led by means of the pipe 11 to the .cooler l2.l From this cooler the liquid is returned to the absorber 2 through the pipe 13 in .which is positioned the pump 14.

In those cases where complete removal of sulphur. 4dioxide from the gaseous mixture is not essential the washer 4 may4 be dispensed with. and the use of glycerol or its equivalent avoided. Under these conditions the gaseous mixture is passed through the absorber 2 containing water to which quinoline is added from time to time at such a rate as to always leave a Surplus of sulphur dioxide content in the water, thus preventing the escape of quinoline with the gases passing over, which obviates the necessity of washing the escaping gas to recover the quinoline. Under these conditions some sulphur dioxide may pass oven-the amount escaping depending on the rate of, passage of the gas through the absorber, the rate of addition of `quinoline and the degree of agitation in the absorber. However, by careful attention the concentration of sulphur dioxide in the water can be maintained at alow value and, as a consequence, the amount of sulphurv dioxide present in the gaseous efliuent is kept low.

vWhat claim as my invention is:

In a process of separating sulphur dioxide from gaseous mixtures the step which consists in bringing the gaseous mixture into intimate contact with -a mixture of, quinoline and water and a diluent medium misciblev with quinoline sulphite. Y

` MAI'ILAND C. BOSWELL;

irs 

